With the emergency of a large-capacity service, a transmission speed of an optical communication transmission network evolves from 40 Gb/s to 100 Gb/s and even 400 Gb/s and 1 Tb/s. In order to achieve a high transmission speed, various advanced modulation formats, for example, PM-QPSK (Polarization Multiplexing-Quadrature Phase Shift Keying, polarization multiplexing-quadrature phase shift keying), QAM (Quadrature Amplitude Modulation, quadrature amplitude modulation), and OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing), are introduced. In another aspect, in order to improve frequency spectrum utilization of an optical fiber and flexibility of system configuration, the optical communication transmission network evolves toward a direction of a variable-bandwidth optical network, that is, a channel interval gradually changes from a fixed channel interval of 100 GHz/50 GHz to a flexibly variable channel interval. FIG. 1A shows a fixed channel interval in an existing optical communication transmission network, and FIG. 1B shows a future development trend of an optical network—a flexibly variable channel interval.
In an optical communication long-distance transmission network, an OEO (Optical-Electrical-Optical) conversion in a system link is in a decreasing trend. It becomes more and more difficult to test a bit error rate in an electrical layer, while a test of the bit error rate merely at a link terminal is not conducive to fault location. With increase of transmission capacity and improvement of flexibility in the optical communication transmission network, a system becomes more and more complex. In order to effectively control and manage an optical network, optical performance monitoring for a high-speed wavelength division multiplexing signal in the optical communication transmission network becomes more and more important. Optical power monitoring can reflect a basic working state of a wavelength channel and instruct the system to perform processing such as automatic power equalization, so that optical power monitoring becomes the most basic and most important performance monitoring content. A typical application scenario of optical power monitoring is shown in the following figure.
In the prior art, technologies for monitoring an optical power of a channel may be generally classified into two types. The first type is that a device such as a grating is used to distinguish light with different wavelengths in terms of space, and a photoelectric detector array is used to detect light intensity at different positions, so as to monitor the optical power and a wavelength of the channel at the same time. The second type is that a TOF (Tunable Optical Filter, tunable optical filter) is used to scan a band to be detected, so as to distinguish light with different wavelengths in terms of time, and then the same photoelectric detector is used to detect an optical power at different time.
In the first type of optical power monitoring technology, first, an optical signal of a certain power is extracted from a network; the optical signal is converted into parallel light after passing through a collimation lens, and the parallel light is incident into a diffraction gating at an optimal diffraction angle of the diffraction grating; after the parallel light passes through the diffraction grating, diffraction light whose diffraction efficiency is quite high is obtained, and optical signals with different wavelengths are separated; the separated optical signals are converged onto different pixels of an array detector after passing through a convergent lens, and are distributed in turn on the array detector according to a wavelength; the array detector performs real-time and rapid sampling on the optical signals, converts amplitude of the optical signals into an electrical signal to obtain original spectrum data, and transfers original data to a signal processor; and the signal processor processes and analyzes the original data, performs a deconvolution operation according to amplitude and distribution of the light intensity, so as to restore a spectrum curve and calculate an optical power of a channel of the optical signal.
In the second type of optical power monitoring technology, a certain optical power is extracted from a signal in the optical communication transmission network and transferred to the TOF; the TOF filters input optical signals, where optical signals with a certain bandwidth pass through the TOF and are introduced into a photoelectric detector; the photoelectric detector performs photoelectric conversion and samples the optical signals, converts amplitude of the optical signals into an electrical signal, and transfers the electrical signal to a signal processing and control apparatus; after receiving sampled data, the signal processing and control apparatus sends an instruction to change a pass-band wavelength of the TOF, repeats the process till a whole required wavelength range is scanned; and finally, the signal processing and control apparatus analyzes and processes obtained sampled data, and performs a deconvolution operation according to amplitude and distribution of the light intensity, so as to restore a spectrum curve and calculate an optical power of a channel of the optical signal.
A principle of calculating a channel power of an optical signal by using a spectrum line that is restored through deconvolution with two existing types of optical power monitoring technologies is introduced briefly in the following with an example. Referring to FIG. 2, FIG. 2 shows typical spectrums of measured signals, where the measured signals are three different rates and formats of signals (10 Gbps NRZ/40 Gbps DQPSK/2.5 Gbps NRZ) at an interval of 50 GHz. A solid line indicates a real spectrum measured by a high-accuracy spectrometer, a “+” symbol indicates an original broadened spectrum obtained after TOF scanning, and a dashed line indicates a spectrum restored through a deconvolution algorithm. After a broadened spectrum is obtained through a deconvolution operation, a power is summed near a peak point of a center wavelength of a channel, so that an optical power of the channel may be obtained. It can be seen from FIG. 2 that, the restored spectrum has a main peak in a place where a signal exists and also has a sidelobe in a place where no signal exists. The sidelobe needs to be distinguished from the signal. In a fixed-bandwidth optical-communication transmission network, because a center wavelength of each channel is fixed and a bandwidth difference is not great, only a main peak at a place of a center wavelength of the restored spectrum needs to be summed to obtain the optical power of the channel.
However, when the optical communication transmission network changes from the fixed-bandwidth optical-communication transmission network to a variable-bandwidth optical-communication transmission network, because a center wavelength is not fixed, a channel bandwidth is indeterminate, a modulation format is indeterminate, and a guard interval between channels is narrow, it is rather difficult to distinguish the main peak and the side-lobe in the restored spectrum to calculate the channel power, so that an error of a monitoring result that is obtained when optical power monitoring is performed by using whether the first type of the optical power monitoring technology or the second type of the optical power monitoring technology is larger, and even the optical power monitoring fails.